Research projects focus on the structureand function of gonadotropin-releasing hormone (GnRH) in reproduction in lampreys. Lampreys and hagfish are the only two living representatives of the most ancient class of vertebrates, the Agnatha. While the basic amino acid sequence of lamprey GnRH has been determined, further studies of the ways in which the hypothalamus exerts its influence on the pituitary-gonadal axis are needed. We propose to determine the regulatory influence of the hypothalamus on the pituitary-gonadal axis by: 1. in vivo and in vitro studies on the actions of GnRH and analogs in lampreys during different reproductive stages; 2. studies on the actions of GnRH and analogs in hypophysectomized lampreys; 3. investigation of the GnRH-binding sites in lamprey brain and pituitary; 4. investigation of seasonal relationships between changes in hypothalamic GnRH and activity of the gonad; and 5. studies on immunoneutralization using antisera directed to lamprey GnRH. Further, we will: 1. collect pituitaries and perform bioassays for the purification of lamprey gonadotropin(s) for the eventual development of a lamprey gonadotropin radioimmunoassay; and 2. to isolate and characterize the second form of lamprey GnRH. Results obtained from these experiments will further our understanding of reproduction in lampreys. In addition, in view of the marked structural difference in lamprey GnRH from other vertebrate GnRHs that have been identified and with the recent availability of lamprey GnRH antibodies, various studies will be undertaken to determine if there is lamprey GnRH-like peptides in representative species of vertebrates to enhance our understanding of the evolution of GnRH peptides.